Number of accidents such as cave-ins, water leakages, and the like, of sewer pipelines and agricultural pipelines is increasing year by year due to corrosion and abrasion or breakage of aging buried pipes. Therefore, there is a demand for appropriate diagnosis of the degree of pipe deterioration, and repair/replacement based on the result of the diagnosis.
In order to diagnose for sewer pipelines and agricultural pipelines, it is generally necessary to put elemental zones constituting an exploration range in order of deterioration level, and find quantitative deterioration p levels, so as to prioritize repair/reconstruction works and determine work methods.
Therefore, conventionally, external appearance is generally checked by visual inspection or a CCTV camera, and if necessary, a core is extracted and a physical property is examined. With such a method, however, only a deterioration which is visually perceived can be detected, a deterioration in the outer circumference or inside of a pipe fails to be found. Therefore, it is difficult to quantitatively detect a deterioration phenomenon as appropriate. It is also necessary to extract a large amount of core so as to collect quantitative data, so that the strength of a sewer pipeline or an agricultural pipeline is impaired, or much time and effort are required to conduct work.
Examination methods for concrete structures may be applicable. For example, a system for estimating a width and a depth of a crack using elastic waves has been proposed (see, for example, Patent Document 1 and Patent Document 2). However, since this examination system utilizes a reduction in the propagation energy of elastic waves or the counted number of elastic waves (the counted number of amplitudes exceeding a predetermined value), the system is easily affected by a situation surrounding a buried pipe, resulting in poor examination accuracy.    Patent Document 1: JP H10-142200 A    Patent Document 2: JP H09-269215 A